4.4.6 The classes file

This file lists the possible classes of Problem Reports. Each line
consists of a class name, followed by a colon and an optional class type
name (the class type name is not used for anything in the current
implementation of gnats, so it may be left blank. The class
and class-type-name fields may only contain alphanumerics,
-, _, and ., but no other
characters.

Then comes another colon, followed by an optional one-line
description of the class. gnats itself does not use the class
description, but external tools such as Gnatsweb and TkGnats may use it.
Therefore, a line in this file should at least contain the following:

class::class description

Lines beginning with # will be ignored, and the first listed
class is the default class for an incoming Problem Report.